1. Field of the Invention
The invention relates to a biaxially oriented multilayer film comprising a base layer and at least one outer layer. The base layer essentially comprises a propylene polymer; the outer layer essentially contains high-density polyethylene (HDPE) and copolymers and/or terpolymers of .alpha.-olefins containing 2 to 10 carbon atoms, optionally mixed with polypropylene. Outer layers disposed on either side may be the same or different. At least one outer layer of the multilayer film is sealable and matt.
The invention also relates to a method of producing a multilayer film and to its use.
2. Description of Related Art
DE-A-16 94 694 discloses sealable multilayer films which are composed of biaxially oriented polypropylene films and contain at least one heat-sealable layer composed of an ethylene/propylene copolymer. These films have good heat sealability, but they are clear and not scratch-resistant to the desired extent. In addition they have inadequate processing properties on fast-running packaging machines.
EP-A-0 008 904 discloses a biaxially oriented three-layer polyolefin film which is sealable on both sides and in which the base layer is formed from propylene polymers and the two sealing layers are formed from sealable olefin polymers. This polyolefin film has good heat sealability, but it is transparent and in particular only slightly scratch-resistant and not printable. In addition, it also leaves something to be desired in relation to its surface slip properties with regard to fast-running packaging machines.
U.S. Pat. No. 4,419,411 discloses a biaxially oriented polyolefin film which is sealable on both sides and contains three layers. In these films, both sealing layers incorporate polysiloxane and silicon dioxide as an additive combination. The base layer is essentially composed of polypropylene and contains a small amount of monocarboxylic acid amide, which partially migrates from the base layer into the two sealing layers. The multilayer polyolefin film described is said to have a particularly low coefficient of friction. This film is particularly subject to the disadvantage that it is not printable.
U.S. Pat. No. 4,578,316 discloses a biaxially oriented multilayer polyolefin film whose base layer is composed of a propylene homopolymer and whose outer layer is composed of a blend of polypropylene and MDPE and/or HDPE. This polyolefin film has a low coefficient of friction combined with a readily wettable surface; however, this film, too, has an excellent optical clarity.
WO 89/10839 describes multilayer polyolefin films whose base layer is composed of a propylene polymer and whose outer layers are composed either of HDPE and an ethylene/propylene copolymer or a polypropylene, the film being stretched under special temperature conditions. It has, in particular, a low coefficient of friction and a good wettability, but at the same time it also has a high gloss and low haze.